Preheat the oven to 350°F (175°C). Grease a 10-inch pie dish.
STEP 2
Melt butter in a skillet over medium heat; add mushrooms. Cook and stir until tender, about 5 minutes. Drain excess liquid, if necessary; set mushrooms aside.
STEP 3
Place sour cream, eggs, Parmesan cheese, flour, heavy cream, onion powder, garlic powder, salt, and hot pepper sauce in a blender; blend until smooth, 30 seconds to 1 minute. Pour mixture into a large bowl.
STEP 4
Stir in mushrooms, Cheddar cheese, and spinach into the egg mixture. Pour into the prepared pie dish.
STEP 5
Bake until lightly browned and a toothpick inserted comes out clean, about 45 minutes.